The Chosen Undead

When Lily messes up the ritual to protect Harry, she protects him WITH death instead of FROM death. When Dumbledore's sensors detect the death of one Harry Potter, he announces the death of the Boy-Who-Didn't-Live-But-Saved-Us-All. So why is it, that fifteen years later, a kid with a shotgun and a scar on his forehead shows up, claiming to be the dead Savior? NOT a Dark Souls xover